A GOVERNMENT investigation is being carried out into the weekend's motorway chaos after a Hampshire MP demanded to know why drivers where left stranded for more than 11 hours.

As previously reported, the M3 near Winchester was closed in both directions on Saturday as police and bomb disposal experts examined “potentially hazardous material” that was found in the carriageway between junctions 9 and 11.

Officers said that tests are still being carried out on the substance to find out exactly what it is after revealing the drama was caused by a piece of flammable material thrown from a bridge in the early hours of Saturday morning.

Hampshire Constabulary also confirmed that a similar incident happened on the same motorway bridge at about 4am on Saturday, September 16 – the week before.

Now transport secretary Chris Grayling approved an investigation into the chaos caused by the incident after Winchester MP Steve Brine demanded to know why drivers weren't better informed of the M3 closure.

Mr Brine said: "Saturday’s incident on the M3 was a nightmare.

"I spoke to the transport secretary and he has agreed to my request for an investigation. That is now underway."

However, a Highways England spokesman defended the organisation's handling of the incident, saying he was driving along the M25 on Saturday when he saw an overhead sign saying the M3 was closed.

He added: “As soon as we were made aware of the incident we set strategic signs and signals informing drivers of the closure.”

In a statement the organisation said it used Twitter, the Traffic England website and bulletins on local and national radio to alert drivers.

But a number of drivers have complained that the warnings weren't good enough. Angela Nickerson, who regularly uses the M3, said: "The trouble is these signs and signals are totally insufficient in number and places to get the information out there. On the A34, which would link up with the M3, for example - where are these signs?

"Also, not everyone uses Twitter. I have never heard of the Traffic England website – and would I be looking at my internet as I was driving? Weekend radio traffic bulletins are few and far between despite there being as much traffic on roads as during the week."